We described a rapid but unambiguous way to distinguish DRB alleles in the rhesus macaque using the polymerase chain reaction, denaturing gradient gel electrophoresis (DGGE) and direct sequencing. The highly variable second exon of Mamu-DRB alleles was amplified using generic DRB primers and alleles were separated by DGGE. DNA was then reamplified from plugs removed from the gel and alleles were determined using fluorescent-based sequencing. Validity of this typing procedure was confirmed by identification of all DRB alleles for three macaques previously characterized by cloning and sequencing techniques. RESULTS Our analysis revealed DRB alleles not previously identified in the three reference animals. Using this technique, we identified 40 alleles in fifteen unrelated macaques. On the basis of phylogenetic tree analyses, 14 new DRB alleles were assigned to 10 different MHC-DRB lineages. Two of the new DRB6 lineages had previously been identified in prosimians and pigtailed macaques. Whereas traditional DRB typing methods provide limited information, our new technique provides a simple and relatively rapid way of identifying DRB alleles for tissue typing, determining individual identification and studies of disease association and susceptibility. OBJECTIVE: To identify rhesus macaque major histocompatibility complex (MHC) alleles for fully understanding models of autoimmune and infectious disease. FUTURE DIRECTIONS This new technique should also contribute to ongoing studies of MHC function and evolution in many different species of nonhuman primates. KEY WORDS Rhesus macaque, DRB1, typing